Noise is one of the factors that may determine the performance of a photosensor arrangement. A photosensor arrangement may be referred to as a pixel.
The full well capacity of a photosensor refers to the total amount of charge that can be stored in the photosensor before overflowing into adjoining photosensors. Since this feature is a result of the photocharge being stored on a capacitor, which is in turn dependent on pixel area, the full well capacity of a photosensor is dependent on its physical size.
Dynamic range is defined as the maximum signal strength detectable by a photosensor divided by the noise in the photosensor. The maximum detectable signal strength by a photosensor is determined by the full well capacity of the photosensor. Furthermore, the noise in the photosensor is the sum of dark and read noise components. In other words, the dynamic range of a photosensor may be described by equation (1) below.Dynamic Range=Full well capacity/SQRT(Dark Noise2+Read Noise2)
Responsivity is a measure of the effectiveness of a photosensor in converting incident electromagnetic radiation into electrical current or voltage, and is inversely related to the capacitance of the photosensor.
There are three main sources of noise that contribute to the degradation of the quality of an image: photon shot noise, dark noise and read noise.
Photon shot noise results from natural fluctuations in the number of photons detected by a photosensor and is caused by the quantum statistical nature of photon emission and detection. This randomness is manifested as a temporal and spatial fluctuation in the signal produced by the photosensor. Photon shot noise occurs even with an ideal noise-free light source and an ideal noise-free photosensor.
Read noise is a combination of system noise components inherent in the conversion of photo generated charge carriers into a measurable signal; processing of the resulting signal; and analog-to-digital (A/D) conversion thereof.
Reset noise is one of the major noise sources when in dark conditions.